The present invention relates to a gas fryer for cooking foodstuffs in cooking oil supplied and heated in an oil tank, more specifically, to a gas fryer comprising a heat pipe in an oil tank and a cooling system for cooling down effectively the exhaust gas from said heat pipe.
Two different types of fryers, that is, a gas fryer and an electromagnetic fryer for cooking foodstuffs in cooking oil are known in the art. A typical gas fryer is a device of heating oil through heat pipes in the oil tank by the combustion gas of burning liquefied natural gas (LNG) or liquefied petroleum gas (LPG). On the other hand, an electromagnetic fryer is a device of heating oil by electromagnetic induction through the heat pipe generating heat by the electric current of a coil. In general, the recovering time (the time for recovering the temperature of oil, from a decreased temperature by adding foodstuffs into the oil tank, to a working temperature) of the gas fryer is shorter than that of the electromagnetic fryer. On the other hand, the temperature of the oil in the tank of the electromagnetic fryer is more uniform than that of the gas fryer (i.e. the low temperature heating which has little difference of the temperature of the oil and that of the heat pipe), thus, the degradation of the oil of the electromagnetic fryer is thought to be lesser than that of the gas fryer.
A gas fryer of such a conventional type comprises, as shown in FIGS. 6 and 7, heat pipes 2 located in an oil tank 1, a combustion chamber 4 from which the combustion gas is blowing from a burner and the like and which is located at the combustion gas inlet side of the heat pipe 2, and a flue 3 from which the combustion gas is exhausted and which is located at the combustion gas outlet side of the heat pipe 2. Almost all parts of said fryer are made of metal sheets such as a stainless steal, in order to improve the thermal conduction. The heat pipes 2 for conducting heat to the oil are located proximate in the middle along the direction of depth of the tank 1 and soaked in the cooking oil, thus, the oil is heated from the middle in the oil tank 1. The temperature of the lower part of the oil is kept as relatively low (approximately 50xc2x0 C.), due to the gentle convection of the oil, therefore, the device is designed as to prevent the oxidation of oil and to be able to keep oil fresh in the long time.
The aforementioned gas fryer also discharges the exhaust gas, generally from the back of the device to outside as it is. Thus, the combustion gas exchanged the heat with the oil in the heat pipe 2, is discharged through the flue 3 as it is, as an exhaust gas holding the temperature of approximately 250 to 350xc2x0 C. The temperature of the flue 3 elevates up to 150 to 250xc2x0 C. by heating with the exhaust gas, the temperature of a backboard 5 also elevates to 100 to 200xc2x0 C. due to the thermal conduction from the flue 3 to the backboard 5.
On the other hand, by heating the oil to 160 to 200xc2x0 C. for cooking foodstuffs, the front panel and sideboard are also heated. A flue jacket 6 functions only as an accessory and for preventing splashes of oil, and an exhaust hole 7 is almost taken up by the flue 3. The air between the flue 3 and the flue jacket 6 is not ventilated.
However, the temperature gradient between the inlet and the outlet side of the heat pipe 2 is rather large in these conventional gas fryer, and a part of the heat pipe near the inlet side of the combustion gas is often over-heated (300 to 350xc2x0 C. in comparison to the setting temperature at 180xc2x0 C.). Thus, it is a problem that the unbalanced temperature causes the degradation of the oil. As the temperature of the oil decreases by adding foodstuffs, the cooking must be interrupted until the decreased temperature recovers to the setting point.
Further, it is also a problem that the working environment is deteriorated by extremely high atmospheric temperature near the fryer due to the extremely high temperature of the exhaust gas from the flue. In addition, the temperature of the flue and the backboard is also extremely high due to the high temperature of the exhaust gas, thus it is also a problem in safety to locate the fryer closely attached to the wall of the cooking facility.
Therefore, it is an object of the present invention to prevent the degradation of cooking oil by improving uneven temperature of a gas fryer. It is a further object of the present invention to increase productivity by reducing the recovering time in a batch of cooking, and the waiting time of workers.
In addition, it is a still further object of the present invention to reduce the temperature of an exhaust gas from the gas fryer efficiently for lowering the temperature of a backboard of the fryer in the safe level.
In view of the above problems, present inventors have studied hard, and found out that the uneven temperature distribution of heat pipes was extremely reduced and the heat-exchange efficiency was extremely improved by preparing the heat pipe, the combustion chamber, the flue and/or a portion thereof with ceramic materials due to the thermal insulation, heat storage, and mixing of the combustion gas.
The present inventors have further found out that the temperature of the exhaust gas can be decreased effectively by providing an introduction system of cool fresh ambient air from outside of the flue. By decreasing the temperature of the exhaust gas effectively, the temperature of the flue can be decreased and the temperature of the backboard near the flue can also be decreased to such a sufficiently safe level that the fryer can be installed in closer to the wall of the cooking facility. These findings have led to the present inventions including the following concrete embodiments.
According to a first aspect of the present invention, there is provided a gas fryer comprising a tank for holding cooking oil, a heat pipe located proximate in the middle depth of said tank so that said heat pipe is soaked in said cooking oil, a combustion chamber located at a combustion gas inlet side of said heat pipe, and a flue located at a combustion gas outlet side of said heat pipe, wherein said heat pipe comprises an insulating sleeve fitted in the inner wall of said heat pipe to prevent direct contact of a combustion gas with the inner wall of said heat pipe, and an insulating spirally shaped mixer installed in said heat pipe, thereby providing approximately homogeneous temperature of said heat pipe.
In a preferred embodiment of the present invention, at least a portion of said sleeve and/or said spirally shaped mixer is made of a ceramic or fire-resistant material.
In a more preferred embodiment of the present invention, said spirally shaped mixer consists of one or more of spiral vanes.
In another preferred embodiment of the present invention, at least a portion of the flue is made of a thermal insulator. A thermal insulator is provided between the combustion chamber and the wall of the tank located proximate to the combustion gas inlet side, and/or the combustion chamber is spatially separated from the tank, or at least a portion of the combustion chamber is made of a thermal insulator for suppressing heat loss. At least a portion of these thermal insulators can be prepared by ceramics.
In a still another preferred embodiment of the present invention, the gas fryer further comprising an entry guide for introducing the combustion gas into the heat pipe, and the entry guide constitute a part of the combustion chamber.
In another embodiment of the present invention, the heat pipe is directly connected to a burner, and whereby at least a portion of the heat pipe functions as the combustion chamber without separate provision of the combustion chamber.
According to a second aspect of the present invention, there is provided a gas fryer comprising a tank for holding cooking oil, a heat pipe located proximate in the middle depth of the tank so that the heat pipe is soaked in the cooking oil, a combustion chamber located at a combustion gas inlet side of the heat pipe, and a flue located at a combustion gas outlet side of the heat pipe, wherein the flue comprises an introduction system of fresh air, the system comprising an blowing nozzle of fresh air positioned proximate to the narrowed region located proximate in the middle of the flue along a longitudinal axis, an inlet of fresh air located on a part of the flue, and a passage of fresh air provided along the inner and/or outer wall of the flue, whereby the exhaust gas is cooled down and the exhaust gas is insulated from the environment around the flue.
In a preferred embodiment of the present invention, the passage of fresh air provided along the inner and/or outer wall of the flue is replaced or added by a passage of fresh air provided by one or more of walls for exchanging the heat between the fresh air and the exhaust gas on or around the top of the inlet of the combustion gas into the flue, and whereby the exhaust gas is cooled down effectively.
Further, in a preferred embodiment of the present invention, there is provided a gas fryer comprising: a tank for holding cooking oil, a heat pipe located proximate in the middle of the tank so that the heat pipe is soaked in the cooking oil, a combustion chamber located at a combustion gas inlet side of the heat pipe, and a flue located at a combustion gas outlet side of the heat pipe, wherein the heat pipe comprises a sleeve fitted in the inner wall of the heat pipe, and a spirally shaped mixer installed in the heat pipe, and wherein the flue comprises an introduction system of fresh air, the system comprising an blowing nozzle of fresh air positioned proximate to the narrowed region located proximate in the middle of the flue along a longitudinal axis, an inlet of fresh air located at a part of the flue, and a passage of fresh air provided along the inner and/or outer wall of the flue.
In another preferred embodiment of the present invention, there is provided a gas fryer comprising: a tank for holding cooking oil, a heat pipe located proximate in the middle depth of the tank so that the heat pipe is soaked in the cooking oil, a combustion chamber located at a combustion gas inlet side of the heat pipe, and a flue located at a combustion gas outlet side of the heat pipe, wherein the heat pipe comprises a sleeve fitted in the inner wall of the heat pipe, and a spirally shaped mixer installed in the heat pipe, and wherein the flue comprises an introduction system of fresh air, the system comprising a blowing nozzle of fresh air positioned proximate to the narrowed region located proximate in the middle of the flue along a longitudinal axis, an inlet of fresh air located on a part of the flue, and a passage of fresh air provided by one or more of walls for exchanging heat between the fresh air and the exhaust gas on or around the top of the inlet of the combustion gas into the flue, and/or provided along the inner and/or outer wall of the flue.